Cavitation evaporator system for oil well fluids integrated with a Rankine cycle

ABSTRACT

Oil field fluids are heated by a cavitation device to minimize or eliminate scaling while reducing their volume by evaporation. Heat is conserved by combining the system with an organic Rankine cycle, which is utilized to rotate or help rotate the cavitation device.

RELATED APPLICATION

This application claims the full benefit of provisional application 61/070,553 filed Mar. 24, 2008, which is specifically incorporated herein in its entirety.

TECHNICAL FIELD

Oil field fluids are heated by a cavitation device to minimize or eliminate scaling while reducing their volume by evaporation. Energy is conserved by combining the system with an organic Rankine cycle.

BACKGROUND OF THE INVENTION

The organic Rankine cycle is well known as a means of converting thermal energy to mechanical energy. Typically the Rankine cycle produces mechanical energy in the form of a turbine turned by the vapor or steam generated in a heat exchanger, where the heat is frequently a low-grade heat source from a different system. An organic Rankine cycle confines a volatile fluid in a closed loop; the fluid is heated to a vapor which is used to turn the turbine, where the vapor condenses, and is returned to the heat exchanger for heating again.

In my U.S. Pat. No. 7,201,225, together with Robert L. Sloan, a cavitation device is used to heat used aqueous oil well fluid in order to conserve the components of the used fluid for recycling. In the process, water is evaporated from the aqueous fluid so the concentrated used fluid can be more easily handled; clean condensate may also be saved or recycled. Waste heat from a Diesel engine or other source of rotational mechanical energy can supplement the heat generated by the cavitation device as the primary means for heating the fluid.

Using waste heat from a Diesel engine or other source of mechanical energy to supplement the heating of an aqueous fluid to be concentrated by evaporation is quite efficient particularly in that the thermal energy transferred to the aqueous fluid reduces the amount of thermal energy that must be generated by the cavitation device for a given quantity of aqueous fluid, but it is not always convenient to adapt a Diesel exhaust, for example, to transfer its heat to the aqueous fluid, nor will this always be the most efficient way to transfer energy into the aqueous fluid. Since the oil well fluid may be separated into three phases, the problem is presented: how best to conserve the thermal energy generated by the cavitation device, while also conserving the components of the fluid and/or reducing the volume of the oil field fluid.

SUMMARY OF THE INVENTION

The present invention takes into account that vapor or steam generated by the cavitation device may be condensed, releasing the latent heat of evaporation, which is a rich source of heat. I utilize heat from the vapor and steam generated by the cavitation device to operate an organic Rankine cycle, which may be referred to hereafter as ORC. As is typical in an ORC, thermal energy of a vapor jet turns a turbine, thus converting the heat into rotational mechanical energy, which may be used to turn the shaft of a generator to generate electricity or to act directly as a source of rotational mechanical energy. The definition of an organic Rankine cycle includes a closed loop of organic (or sometimes other) fluid which is alternately boiled and condensed; being in a closed loop, the organic fluid is separate from the oil well fluid, but I have integrated the two systems to save thermal energy by using the heated well fluid to heat the organic fluid of the Rankine cycle, as will be explained in more detail below.

The term “oil field fluid” as used herein should be understood to include not only oil field brines which are formulated and used as completion and workover fluids, but also used drilling fluids (also formulated) and especially to include produced fluids—fluids originating in the earth's formations and brought to the earth's surface through a wellbore. The term “oil well fluid” may be considered synonymous. My invention is useful to reduce the volume of any of these, to simplify handling, for reuse, or for other purposes as may be seen below. In the drawings, brine is used only as an example of an oil well fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram flow sheet showing the oil well fluid heated by the cavitation device passing through a heat exchanger used to vaporize a working fluid in the Rankine cycle.

FIG. 2 is a block diagram flow sheet showing only the vapor obtained by heating in the cavitation device passed to the heat exchanger for the Rankine cycle.

FIG. 3 illustrates, in another block diagram flow sheet, the use of a Rankine cycle to power the cavitation device on a site having a source of natural gas.

DETAILED DESCRIPTION OF THE INVENTION

In the description below, it is to be understood that cavitation devices are designed deliberately to generate heat by cavitation. Cavitation occurs in a fluid when the fluid flows in an environment conducive to the formation of partial-vacuum spaces or bubbles within the fluid. Since the spaces or bubbles are partial vacuum, they almost immediately implode, causing the mechanical or kinetic energy of the fluid to be converted into thermal energy. In many devices, such as most pumps, cavitation is an occurrence to be avoided for many reasons, not least because of convulsions and disruption to the normal flow in the pump, but also because of the loss of energy when the mechanical energy of the pump is converted to undesired heat instead of being used to propel the fluid on a desired path. There are, however, certain devices designed deliberately to achieve cavitation in order to increase the temperature of the fluid treated. Such cavitation devices are manufactured and sold by Hydro Dynamics, Inc., of Rome, Ga., most relevantly the devices described in U.S. Pat. Nos. 5,385,298, 5,957,122, 6,627,784 and particularly U.S. Pat. No. 5,188,090, all of which are hereby specifically incorporated herein by reference in their entireties. These patents may be referred to below as the HDI patents.

The basic design of the cavitation devices described in the HDI patents comprises a cylindrical rotor having a plurality of cavities bored or otherwise placed on its cylindrical surface. The rotor turns within a closely proximate cylindrical housing, permitting a specified, relatively small, space or gap between the rotor and the housing. Fluid usually enters at the face or end of the rotor, flows toward the outer surface, and enters the space between the concentric cylindrical surfaces of the rotor and the housing. While the rotor is turning, the fluid continues to flow within its confined space toward the exit at the other side of the rotor, but it encounters the cavities as it goes. Flowing fluid tends to fill the cavities, but is immediately expelled from them by the centrifugal force of the spinning rotor. This creates a small volume of very low pressure within the cavities, again drawing the fluid into them, to implode or cavitate. This controlled, semi-violent action of micro cavitation brings about a desired conversion of kinetic and mechanical energy to thermal energy, elevating the temperature of the fluid without the use of a conventional heat transfer surface. The heat generated by the cavitation process is augmented by heat generated by friction as the fluid moves relative to the rotor and stator.

Benefits of the HDI cavitation devices include that they can handle slurries as well as many different types of solutions, they can be used to concentrate such slurries and solutions by facilitating the removal of steam and vapor from the fluid being treated, and the heating of the fluid occurs within the fluid itself rather than on a heat exchange surface which is likely to be vulnerable to scale formation and ultimately to a significant reduction in heat transfer.

Definition: I use the term “cavitation device” to mean and include any device designed to impart thermal energy to flowing liquid by causing bubbles or pockets of partial vacuum to form within the liquid it processes, the bubbles or pockets of partial vacuum being quickly imploded and filled by the flowing liquid. The bubbles or pockets of partial vacuum have also been described as areas within the liquid which have reached the vapor pressure of the liquid. The turbulence and/or impact, sometimes called a shock wave, caused by the implosion imparts thermal energy to the liquid, which, in the case of water, may readily reach boiling temperatures. The bubbles or pockets of partial vacuum are typically created by flowing the liquid through narrow passages which present side depressions, cavities, pockets, apertures, or dead-end holes to the flowing liquid; hence the term “cavitation effect” is frequently applied, and devices known as “cavitation pumps” or “cavitation regenerators” are included in our definition. Steam generated in the cavitation device can be separated from the remaining, now concentrated, water and/or other liquid which frequently will include significant quantities of solids small enough to pass through the device. The term “cavitation device” includes not only all the devices described in the above itemized HDI U.S. Pat. Nos. 5,385,298, 5,957,122 6,627,784 and 5,188,090 but also any of the devices described by Sajewski in U.S. Pat. Nos. 5,183,513, 5,184,576, and 5,239,948, Wyszomirski in U.S. Pat. No. 3,198,191, Selivanov in U.S. Pat. No. 6,016,798, Thoma in U.S. Pat. Nos. 7,089,886, 6,976,486, 6,959,669, 6,910,448, and 6,823,820, Crosta et al in U.S. Pat. No. 6,595,759, Giebeler et al in U.S. Pat. Nos. 5,931,153 and 6,164,274, Huffman in U.S. Pat. No. 5,419,306, Archibald et al in U.S. Pat. No. 6,596,178 and other similar devices which employ or include a shearing effect between two close surfaces, at least one of which is moving, such as a rotor, and/or at least one of which has cavities of various designs in its surface (a cavitation zone) as explained above. Shearing and turbulence commonly occurs in cavitation devices, and possibly should not be ignored in considering their heat generating abilities, but most of the thermal energy imparted to the liquid in a cavitation device is by way of cavitation, by definition.

In FIG. 1, the oil well brine or other oil well fluid enters the cavitation device 1 from conduit 2. The fluid is heated in the cavitation device 1 to a degree which is a function of the flow rate of the fluid, the properties of the cavitation device, and the mechanical input by rotation of the shaft driving the rotating drum inside the cavitation device. After the particular cavitation device has been selected, the operator can control the heating process in the cavitation device by manipulating the flow rate of the oil well fluid into the cavitation device 1, the speed of rotation of the rotor within it, and the proportion of recycle in line 3. Line 3, with appropriate valves, permits the operator to recycle a portion of the fluid to the entrance of the cavitation device 1, which further elevates its temperature. While the cavitation device is capable of raising the fluid temperature to the atmospheric boiling point, the boiling point of the fluid may be lowered by pulling a vacuum on the output line 4 (or 10) from the cavitation device 1.

In the configuration of FIG. 1, output line 4 leads directly to heat exchanger 5. The purpose of heat exchanger 5 is to transfer thermal energy from the fluid in output line 4 to the organic or other working fluid in the closed loop organic Rankine cycle. As is known in the art, the fluid of an organic Rankine cycle is contained in a closed loop, in this case marked ORC and represented by conduit 6 leading to the heat exchanger 5 and passing through it, and conduit 7, carrying heated organic fluid from the heat exchanger 5 to turbine 8. At turbine 8, one or more jets of vaporized organic fluid are directed toward flanges on the turbine 8 in a known manner, causing the turbine to rotate, converting the latent heat of evaporation in the vapor to mechanical energy, resulting in condensation of the fluid. In turbine 8, the condensed fluid is collected and then returned through conduit 6, which returns the fluid to heat exchanger 5.

The mechanical work generated by the impact and condensation of the vapor on turbine 8 is seen to be transmitted directly to a square 9 labeled “MECH POWER,” by the rotation of shaft 15. Rotating shaft 15 may be connected directly or through appropriate gearing to an electric motor or Diesel engine, for example, being used to rotate the rotor in cavitation device 1. This mechanical input will directly reduce the work necessary for the motor or engine to perform. Alternatively, shaft 15 may rotate the rotor of an electric generator, the output of which is used to turn the cavitation device 1 together with current from a public grid or other source of electricity, the input of each being continuously apportioned by known computer or other means according to the demand of the cavitation device 1 and the output of the turbine 8. Or, the electricity output of such a generator may be used to supplement the power for a vacuum pump used to remove vapor from line 4, again with an appropriate control system.

Where the turbine 8 is used to operate an electric generator whose output is intended to supplement the original (such as from a grid or a primary power source brought to the site on a skid) power input to the motor driving the cavitation device 1, the motor may be equipped with a variable frequency drive to reduce the original power input as a function of the power made available by the turbine 8. Alternatively, as is known in the art, an automated switch may be programmed to supplement the original power input with power available within a predetermined range from the turbine operated generator.

The organic or other fluid in conduits 6 and 7 may be any fluid capable of evaporation and expansion when heated and readily converting its latent heat of evaporation into mechanical energy in a turbine, followed by condensation. The fluids used in an ORC are sometimes referred to as “working fluids.” Examples are pentane, isopentane, butane and isobutene, but many such fluids are known, some of which are not necessarily organic, such as ammonia. Generally, they will have a lower heat of vaporization than water. I am also aware of certain closed loops having a purpose similar to the Rankine cycle, such as the Kalina cycle, which commonly uses more than one vaporizable material and frequently more than one closed loop. My invention contemplates the use of any closed loop wherein at least one fluid is circulated for heating to vaporization by absorbing heat in a heat exchanger and then converting that heat energy to mechanical work by striking a turbine to rotate it, thereby condensing the fluid and returning it to the heat exchanger.

Referring again to FIG. 1, as indicated above, thermal energy in the oil well fluid (in this case brine) in line 4 is transferred to the organic fluid in conduits 6 and 7 in heat exchanger 5, and the oil well fluid continues in line 10 to phase separator 11. Phase separator 11 is represented as a block on this flowsheet, as there are numerous techniques for separating the solids, concentrated liquid, and gas or vapor in the oil well fluid at this point. Even though significant condensation will have taken place when passing through heat exchanger 5, and bearing in mind that use of a vacuum is recommended to facilitate a reduced boiling temperature and, accordingly, enhanced vapor generation, there may be substantial remaining aqueous vapor from the oil well fluid, and this may be released to atmosphere through line 12. The vapor in line 12 may also be led to a condenser or an additional heat exchanger to conserve the thermal energy; the additional heat exchanger may provide additional heat to the organic Rankine cycle or it may help to increase the temperature of the incoming oil well fluid in conduit 2.

Provision for separating solids in the oil well fluid, such as a filter, are also contemplated in phase separator 11, as indicated by line 13, representing the removal of the solids. Removal may also be accomplished by a centrifuge, or by settling, as in a settling tank. Solids removed through line 13 in FIG. 1 can be discarded or, in some cases, treated for recovering valuable components of the oil well brine that may adhere to solid particles. Whether or not solids are removed in a separate step, the fluid in line 4, after passing through heat exchanger 5, may be sent to an optional membrane evaporator—that is, a device including a membrane capable of passing only water vapor and not liquid water.

Aqueous liquid concentrate may be removed from phase separator 11 through line 14. The concentrated aqueous fluid will frequently contain valuable components which can be recovered in a separate process. Or, the concentrate may be recycled—used with or without significant adjustment, as the basis for a new oil well fluid. For this purpose, line 14 may pass through automatic analyzers, such as an analyzer for chloride or bromide content, or for zinc content, and adjustments can be made more or less as described in the aforementioned Smith and Sloan U.S. Pat. No. 7,201,225, which is hereby expressly incorporated herein in its entirety.

FIG. 2 describes a variant of my invention also comprising a closed loop, specifically an organic Rankine cycle, and a system for reducing the volume of oil well fluid, in which the oil field fluid and the Rankine cycle fluid are kept separate. As in FIG. 1, the organic Rankine cycle includes a closed loop comprising conduits 6 and 7. Conduit 6 leads into and through heat exchanger 20 and conduit 7 leads into turbine 8. Here, line 21, carrying heated brine or other oil field fluid from the cavitation device 22, leads directly to a flash tank 23 rather than to a heat exchanger such as FIG. 1's heat exchanger 5. Flash tank 23 has a line 24 for directing vapor therefrom to heat exchanger 20, where it yields substantial latent heat as the heat of evaporation and then proceeds to a condensate collector and/or a condenser for any remaining vapor. Line 24 is desirably connected to a vacuum pump not shown, which will keep the vapor moving through line 24 but also will reduce the boiling point of the fluid in the flash tank 23. Flash tank 23 is seen to contain concentrated liquid 27—that is, the oil well fluid has become concentrated by the removal of the vapor through line 24. At the same time, solids entering the cavitation device 22 with the used oil well brine in line 28 will pass through the cavitation device 22 to flash tank 23 and tend to settle in it. The solids can be intermittently or continuously removed through line 29 for discarding or other uses. Concentrated liquid 27 can be removed continuously or intermittently through line 30, and can be treated to recover valuable components or recycled in any desired proportion by sending it back to the cavitation device 22 through a recycle line 31 similar to recycle line 3 in FIG. 1.

As in the configuration of FIG. 1, the work performed by turbine 8 in FIG. 2 may be utilized in various ways, such as by supplementing mechanical power source 9, through rotating shaft 15 which is represented as continuing on to provide rotational power for cavitation device 22. Computers, control devices, gear transmissions, relays and the like, not shown, may be used to transmit the thrust of the turbine 8 to cavitation device 22, directly or indirectly, in response to demand from the cavitation device or as a supplement to a primary source of rotational power for the cavitation device 22. As with the configuration of FIG. 1, an automatic switch, or a variable frequency device may be used to proportion the power available to the cavitation device between the base original power and that generated by the turbine.

In the flowsheet of FIG. 3, the cavitation device 40 receives an oil well fluid, in this case produced fluid, through line 41, and heats it by cavitation as explained above. The heated fluid is sent to flash tank 42 through line 43. Vapor or steam is removed from the flash tank 42 through line 44 with the possible aid of a vacuum pump not shown, and sent to heat exchanger 45, where it gives up its latent heat of evaporation, producing a condensate of clean water which is removed through line 46 for storage or use as clean water for any of many purposes. Concentrated fluid 48 in the lower portion of flash tank 42 may be removed through line 59 for storage, further treatment such as recovery of valuable components, or reuse in a well. Accumulated solids can be removed continuously or intermittently through line 47, similar to line 29 in FIG. 2. Also passing through heat exchanger 45 is Rankine cycle conduit 49, containing the Rankine cycle working fluid, which picks up heat from the vapor in line 44, condensing it in the process as mentioned above. Conduit 49 leads to heat exchanger 50, which provides thermal energy from the exhaust of engine 51, using as fuel natural gas, Diesel fuel, or other hydrocarbon fuel. Engine 51, through shaft 58, operates a compressor 52 for natural gas in line 53. The natural gs may come from any source—for example, a separate gas well, a gas storage area, gas which is coproduced from an oil well, a transmission line near a recompression station, or other source. The compressed natural gas is sent from compressor 52 through yet another heat exchanger 54, where the gas gives up heat of decompression as it enters natural gas transmission line 55 or a pipeline leading to any destination. Heat exchanger 54 thus contributes heat to the working fluid of the Rankine cycle in conduit 49. Conduit 49 continues from heat exchanger 50 to a turbine 56, where the working fluid, which has become a vapor, is used to rotate the turbine, converting its latent heat into rotational mechanical energy, in the form of a shaft 57 which is used to turn the rotor of cavitation device 40. As in FIGS. 1 and 2, the rotational force of the turbine may be used to operate an electrical generator which can run a motor for operating the cavitation device; also, and alternatively, the mechanical work done by the turbine may be allocated to the cavitation device in response to demand as a supplement to other sources of power. Where power for operating the cavitation device is to be shared, it may be desirable to establish controls that utilize first all of the power provided by the turbine, supplemented by power from the grid or other plentiful source. As indicated with respect to FIGS. 1 and 2, an automated switch or variable frequency drive may be used. Any technique or device for efficiently utilizing the mechanical or electrical power generated by turbine 56 to help run the cavitation device 40 may be used.

It should be understood that pumps, valves, controls and the like necessary for the systems of FIGS. 1, 2, and 3 to function are not illustrated because they may vary considerably with the engineering designs and the discretion of the operators of the particular applications of the invention. The amount and kind of oil well fluid, the availability of exhaust heat on site, and the objectives of the operators in terms of energy and material conservation will affect the choice of the ORC working fluid, the size and flow rating of the cavitation device, and the amount of vacuum to pull on the vapor phase of the cavitation device are all significant factors but within the skill of the art. Likewise the kinds of heat exchangers and their deployment can vary considerably. I do not intend to be limited to the particular configurations shown and described herein.

Thus my invention includes an apparatus for reducing the volume of an oil field fluid comprising (a) an organic Rankine cycle comprising (i) a circulating volatile fluid, (ii) a heat exchanger for vaporizing the volatile fluid, and (iii) a turbine for converting the latent heat of the vaporized fluid to mechanical work, and (b) a system for vaporizing at least a portion of the oil field fluid comprising (i) a cavitation device for heating the oil field fluid, (ii) means for passing at least a portion of the oil field fluid so heated through the heat exchanger in heat exchange relation, and (iii) means for removing at least a portion of the heated oil field fluid from the apparatus as vapor or condensate therefrom.

My invention also includes a method of reducing the volume of an aqueous oil field fluid comprising (a) heating the oil field fluid in a cavitation device, (b) removing water vapor from the oil field fluid heated thereby, (c) condensing the vapor in a heat exchanger and utilizing the latent heat of evaporation obtained in the heat exchanger to vaporize a volatile fluid in a Rankine cycle, (d) rotating a turbine to generate rotational force by applying the vaporized volatile fluid thereto, and (e) utilizing the rotational force as work applied in at least one of steps (a), (b), and (c).

My invention also includes a method of reducing the volume of oil field fluid comprising (a) transferring waste heat energy from a compressor for natural gas to a fluid confined in an organic Rankine cycle, (b) converting the heat energy to mechanical power by releasing the heat energy to a turbine in the organic Rankine cycle, (c) utilizing the mechanical power to operate a cavitation device, (d) feeding the oil field fluid to the cavitation device to heat the oil field fluid, and (e) separating water vapor from the oil field fluid so heated. 

1. Apparatus for reducing the volume of an oil field fluid comprising (a) an organic Rankine cycle comprising (i) a circulating volatile fluid, (ii) a heat exchanger for vaporizing said volatile fluid, and (iii) a turbine for converting the latent heat of said vaporized fluid to mechanical work, and (b) a system for vaporizing at least a portion of said oil field fluid comprising (i) a cavitation device for heating said oil field fluid, (ii) means for passing at least a portion of the oil field fluid so heated through said heat exchanger in heat exchange relation, and (iii) means for removing at least a portion of said heated oil field fluid from said apparatus as vapor or condensate thereof.
 2. Apparatus of claim 1 including a shaft on said turbine in work transmitting relation to said cavitation device.
 3. Apparatus of claim 1 wherein said turbine is connected to an electrical generator to convert the mechanical work of said turbine to electric power.
 4. Apparatus of claim 3 including means for applying said electric power to said cavitation device.
 5. Apparatus of claim 1 wherein said system (b) for vaporizing includes a flash tank.
 6. Apparatus of claim 1 including at least one heat exchange device for transferring waste heat from at least one power source other than said cavitation device.
 7. Apparatus of claim 1 wherein said means (b)(iii) for removing at least a portion of said heated oil field fluid as vapor or condensate comprises a vacuum pump.
 8. Method of reducing the volume of an aqueous oil field fluid comprising (a) heating said oil field fluid in a cavitation device, (b) removing water vapor from the oil field fluid heated thereby, (c) condensing said vapor in a heat exchanger and utilizing latent heat of evaporation obtained in said heat exchanger to vaporize a volatile fluid in a Rankine cycle, (d) rotating a turbine to generate rotational force by applying said vaporized volatile fluid to said turbine, and (e) utilizing said rotational force in at least one of steps (a), (b), and (c).
 9. Method of claim 8 wherein said rotational force is utilized to generate electric power.
 10. Method of claim 9 wherein said electric power is applied to a motor used to operate said cavitation device.
 11. Method of claim 8 wherein said rotational force is applied to said cavitation device,
 12. Method of claim 8 wherein said rotational force is applied to a pump.
 13. Method of claim 8 including providing additional heat from a waste heat source for vaporizing said volatile fluid in said Rankine cycle.
 14. Method of claim 8 wherein the water vapor removed in step (b) is removed at least partly by applying a vacuum to said heated oil field fluid.
 15. Method of reducing the volume of oil field fluid comprising (a) transferring waste heat energy from a compressor for natural gas to a fluid confined in an organic Rankine cycle, (b) converting said heat energy to mechanical power by releasing said heat energy to a turbine in said organic Rankine cycle, (c) utilizing said mechanical power to operate a cavitation device, (d) feeding said oil field fluid to said cavitation device to heat said oil field fluid, and (e) separating water vapor from the oil field fluid so heated.
 16. Method of claim 15 wherein the water vapor of step (e) is separated at least partly by applying a vacuum to said heated oil field fluid. 